1. Field of the Invention
The present invention relates to an evacuation method and a storage medium, and more particularly, to an evacuation method for a vacuum processing apparatus including a vacuum processing chamber with moisture attached to a wall and a component surfaces of the chamber.
2. Description of the Related Art
A vacuum processing apparatus, for example, a plasma processing apparatus, includes a vacuum processing chamber that accommodates a wafer as a substrate and performs plasma processing, such as etching, on the wafer. When plasma processing is repeatedly performed, deposits are attached to the wall and the component surfaces of the chamber. To remove such deposits on a regular basis, it is necessary to clean the wall and the component surfaces, specifically, wipe them with a cloth containing alcohol or other solvents. In this process, since an operator needs to access the internal space of the chamber with his/her arm, the chamber is exposed to the atmosphere. When the chamber is exposed to the atmosphere, moisture in the atmosphere is attached to the wall and the component surfaces of the chamber.
After the cleaning, the chamber is evacuated. However, after the air and other gases are discharged from the chamber, the moisture attached to the wall and the component surfaces is evaporated and released (degassed), disadvantageously resulting in an increased time required for the evacuation.
To reduce the time required for the evacuation, a variety of evacuation methods have been developed. For example, in one of such methods, after the evacuation is initiated, a dry inert gas is temporarily introduced into the chamber to create a positive pressure state, the positive pressure being at least the atmospheric pressure, and then the evacuation is continued (see Japanese Laid-Open Patent Publication (Kokai) No. 2002-249876). According to this method, the introduction of the dry inert gas facilitates sweeping and replacing the moisture attached to the wall, and hence the evacuation time is reduced.
However, even when the above evacuation method is used, after the chamber has been depressurized and the air and other gases have been discharged, the moisture attached to the wall and the component surfaces begins to evaporate. Further depressurization of the chamber causes adiabatic expansion, so that the temperature of the moisture decreases and eventually becomes below zero degrees. In this state, the moisture that has not evaporated may solidify.
The moisture that has solidified will not readily evaporate during the evacuation (in fact, the present inventor has conducted an experiment and found that the discharged gas has the greatest amount of moisture at a pressure around a target pressure of 1.3×10−3 Pa (1×10−5 Torr)). That is, the moisture that has solidified keeps evaporating but confines moisture that has not solidified and been housed in tiny recesses formed in the wall and other surfaces for an extended period of time. Therefore, the evacuation still disadvantageously requires a long period of time even if the above-mentioned method is used.
Further, the moisture that has solidified causes other moisture-related problems, for example, generation of particles, abnormal discharge, and erosion of the components.